Heretofore, for example, when a constituent element of an automobile or the like is welded, a clamp apparatus has been used in order to clamp the constituent element. Such a clamp apparatus includes a main body, a cylinder connected to the main body, and a clamp arm, which is rotated a predetermined angle, under a driving action of the cylinder, through a toggle link mechanism disposed inside of the main body. In addition, by displacing a piston and piston rod of the cylinder in an axial direction by means of a pressure fluid supplied to the cylinder, via the toggle link mechanism connected to the piston rod, the clamp arm is rotated through an operating angle based on the displacement amount of the piston. As a result, switching can occur between a clamped state, in which the workpiece can be clamped, and an unclamped state in which the clamped state of the workpiece is released.
On the other hand, with the aforementioned clamp apparatus, there is frequently a desire to arbitrarily adjust the operating angle of the clamp arm, for example, corresponding to the state under which the clamp apparatus is used. For this purpose, a clamp apparatus is known having an angle adjusting mechanism, which is capable of adjusting the operating angle of the clamp arm.
As one type of angle adjusting mechanism for a clamp apparatus, as disclosed in the specification of French Patent Application No. 9712535, a sub-rod is threadedly engaged with a piston rod connected to a piston, wherein a toggle link mechanism is connected with respect to the sub-rod. In addition, by threaded rotation of the sub-rod with respect to the piston rod, the length of the piston rod and sub-rod is made freely adjustable, wherein based on displacement of the piston rod, the operating angle of the rotating clamp arm is adjusted.
Further, in the angle adjusting mechanism of the clamp apparatus disclosed in U.S. Pat. No. 6,557,841 B2, a plurality of grooves, separated at equal intervals, are formed on the outer circumferential surface of the sub-rod disclosed by the aforementioned French Patent Application No. 9712535. After the sub-rod has been displaced along the piston rod for adjusting the length of the piston rod and sub-rod, an engaging ring engaging with the piston rod engages within the grooves for regulating displacement of the piston rod and the sub-rod, thereby integrally fixing the piston rod and the sub-rod to each other.
Further, in the angle adjusting mechanism of the clamp apparatus disclosed in U.S. Pat. No. 6,612,557 B2, a structure is provided in which threads are engraved along the outer circumferential surface of the piston rod connected to the piston, wherein the threads of the piston rod are screw-engaged with an inner part of a tubular member connected with the toggle link mechanism. Further, by threaded rotation of a rod screw, which is exposed on an outer body portion, the overall length of the piston rod and the tubular member can be adjusted.
Still further, in an angle adjustment mechanism of a clamp apparatus, as disclosed in German Patent Document No. 19824579 C1, a displaceable head cover is provided in the interior of a cylinder, wherein during unclamping, displacement of the piston can be regulated through the head cover. In addition, a displacement amount of the piston is regulated by first displacing the head cover freely along the cylinder, and then fixing the position of the head cover by an adjustment bolt, for thereby adjusting the operating angle of the clamp arm that is rotated by a displacement action of the piston.
However, in the techniques disclosed in the aforementioned French Patent Application No. 9712535 and U.S. Pat. No. 6,557,841 B2, when the operating angle of the clamp arm is adjusted, it is necessary that the sub-rod and tubular member disposed inside the cylinder be screw-rotated or engaged by means of an engagement ring onto the piston rod. As a result, in the case that an angular adjustment of the clamp arm is performed, the clamp apparatus must first be dismantled, whereupon the adjustment operation is carried out, and hence the angular adjustment operation is extremely complicated. Further, it is impossible to perform the adjustment operation while confirming the operating angle of the clamp arm.
Furthermore, in the technique according to U.S. Pat. No. 6,557,841 B2, since the sub-rod cannot be locked with respect to the piston rod except at the position of the grooves, the length of the piston rod and sub-rod cannot be set arbitrarily. As a result, the adjustable range for the operating angle of the clamp arm is limited.
Further, in the technique disposed in U.S. Pat. No. 6,612,557 B2, a structure is provided whereby the angle of the clamp arm is adjustable from the exterior. However, since a mechanism for regulating rotation of the rod screw is not provided, after an adjustment is performed by means of the rod screw, there remains a concern that the rod screw may be rotated in error, thus altering the set angle that was adjusted.
On the other hand, in the technique disclosed by German Patent Document No. 19824579 C1, a switch that detects the operating angle of the clamp arm is installed in the head cover. Owing thereto, when the head cover is displaced, the switch is displaced integrally with the head cover, accompanied by movement of the lead wires connected to the switch. As a result, it is necessary for the length of the lead wires to be set longer beforehand, which tends to be troublesome.